<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <!-- <script>
        alert('Hello World!');
    </script> -->
    <!--外部引入，注意：script标签必须成对出现 -->
    <script src="js/dn.js"></script>
    <!--注意：不写type也默认是javascript -->
    <script type="text/javascript">
        //hello; 注释和java一样
    </script>
</head>
<body>

</body>
</html>